feat: Add pathlib.Path normalization to string representation

[smortezah]

Description

Added support for normalizing common Python types (pathlib.Path objects) to JSON-compatible values during TOON encoding. This enhancement makes it easier to serialize Python applications that work with file paths.

Type of Change

• New feature (non-breaking change that adds functionality)
• Test coverage improvement

Related Issues

Closes # (if applicable)

Changes Made

• Extended normalize_value() function in src/toon_format/normalize.py:

  • Added pathlib.Path, PurePath, PurePosixPath, PureWindowsPath → string conversion
  • Updated module docstring to document new type conversions
  • Added detailed examples in function docstring

• Added comprehensive test coverage in tests/test_normalization.py:

  • TestPathNormalization class with 5 tests covering Path object handling

SPEC Compliance

• This PR implements/fixes spec compliance
• Spec section(s) affected: Section 3 (Normalization) - extends Python-specific normalization
• Spec version: v1.5 (maintains compatibility while extending Python support)

Testing

• All existing tests pass
• Added new tests for changes
• Tested on Python 3.8
• Tested on Python 3.9
• Tested on Python 3.10
• Tested on Python 3.11
• Tested on Python 3.12

Test Output

$ pytest tests/test_normalization.py::TestPathNormalization -v
======================== test session starts =========================
collected 5 tests

tests/test_normalization.py::TestPathNormalization::test_path_to_string PASSED
tests/test_normalization.py::TestPathNormalization::test_relative_path PASSED
tests/test_normalization.py::TestPathNormalization::test_pure_path PASSED
tests/test_normalization.py::TestPathNormalization::test_path_in_array PASSED
tests/test_normalization.py::TestPathNormalization::test_path_in_nested_structure PASSED

$ pytest tests/ -v
======================== 818 passed, 13 skipped in 2.34s =========================